Telephone exchange system



' June 30, 1931. J, H, E, BAKER' 1,812,617

TELEPHONE EXCHANGE SYSTEM Filed Feb. 20, 1930 4 SheetsSheet 1 //VVEN7'0R. Ll. hi 5. BAKER A Tram/5r June 30, 1931. J. H. E. BAKER 1,812,617

TELEPHONE EXCHANGE SYSTEM Filed Feb. 20, 1950 4 Sheets-Sheet 2 //v VENTU/i J hf E. 5/1 KER BY waa w A T TUBA/EX June 30, 1931. J. H. E. BAKER 1,312,617

TELEPHONE EXCHANGE SYSTEM Filed Fb. 20, 1930 4 Sheets-Sheet 3 A r TUBA/EX June 30, 1931. K R 1,812,617

TELEPHONE EXCHANGE SYSTEM Filed Feb. 20, 1930 4 Sheets-Sheet 4 A 7'TORNEX Patented June 30, 1931 UNITED sTArss PTENT OFFICE JOHN H. E. BAKER, OF ALDWYCH, LONDON, ENGLAND, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK TELEIEHONE EXCHANGE SYSTEM Application filed February 20, 1930, Serial No. 429,945, and. in Great Britain February 21, 1929.

This invention relates to automatic telephony and particularly to systems employing step-by-step selector switches of the Strowger type. Heretofore, in such systems,

where switches are set directly in response to the subs-cribers dial, the most common practice has been to use one selector switch for each d1g1t swltchmg stage except. the last two, and to use a final connector switch there out the use of a central office sender having registering and controlling mechanism.

To attain this object, use is made of a 400 point Strowger switch as a group selector while a. similar switch is used as a connector.

Each group selector is provided with four sets of three wipers each and is used in connection with a control circuit common to a number of group selectors. Similarly each connector is provided with four sets of three wvipers each and is used in connection with a control circuit common to a number of connectors. A connection is extended over a group selector switch and a final connector switch by the selection, in each case, of a particular one of the four wiper sets, the. s lection of the Wiper set in the group selector being eifected by the control circuit associated with that selector from the registration therein of the hundreds digit while the selection of the'wiper set in the connector is eliected by its common control circuit through a record of the thousands and hundreds digits transmitted to it by the group selector control circuit from the registration therein recorded of both of these digits. The control circuit associated with the group selector does not record the complete registration of the number of the wanted line but, as already indicated, only of the thousands and hundreds digits. By using a five digit numbering system with the present invention, the first digit may be made to discriminate between an interoffice and a local call, the first digit being efiective only in the former case, while it is absorbed for the latter.

In accordance with the present invention therefore, one specific embodiment of which is disclosed herein by way of illustration, this is accomplished in the following improved manner: A number of 400 point switches are used as group selectors and are wired in multiple to a common control circuit through two relays of association in each group selector switch. These group selectors are made accessible to calling subscribers by any well known means, as for instance, the individual line and master switch arrangement commonly used in automatic systems employing Strowger apparatus. The seizure of an idle group selector by a calling subscriber presupposes the idle condition of the control circuit associated therewith, so that, when a group selector is taken into use and the relays of association are operated, the remaining group selectors using this control circuit are temporarily made busy until the control circuit is free again to be used with any other group selector of the group.

The subscriber proceeds to dial the wanted number and the first digit of the five digit number, a five digit numbering system being here used for illustration, discriminates be-' tween a local and an interoiiice call. Should the call be local the ten thousands digit causes the switch shaft carrying the four wiper sets to be stepped vertically to a p redetermined trunk level of the switch bank whereupon it releases and restores to normal. On the other hand, if the call is for a subscriber in another oiiice, the ten thousands digit steps the switch shaft vertically to the level called for by that digit but in no, case up to the predetermined level for a local connection. In the case of a local call, when the switch shaft of the group selector has restored to normal, it thereafter follows the impulses of the thousands digit, the switch shaft being raised to the levelcorresponding to the digit dialed. A the same time the digit is recorded in the'control circuit. The hundreds digit, when dialed, is also recordedin the control circuit and by a circuit arrangement to be described hereinafter, the record of the hundreds digit in the control circuit causes the selection of one of the wiper sets of the group selector, thereby causing the group selector to connect with a trunk group leading in the wanted direction thru the selected wiper set and trunk switch bank accessible to it. The switch shaft is then rotated for the selection of an idle trunk line in that level; the testing for an idle trunk taking place through one of the three wipers of the selected wiper set.

lVhen such a trunk is found and connection to a connector switch is established, this connector switch is operatively associated with its idle control circuit by the operation of a relay of association. The thousands and hundreds digits, registered in the group selector control circuit, are now transmitted to and recorded in the connector control circuit by an appropriate code. This record causes the selection of that one of the four wiper sets of the connector switch having access to the group of one hundred subscribers in which the wanted subscribers line is located. It is to be noted that this operation of associating the common control circuit with the selected connector switch, as well as the transmission and registration therein of the thousands and hundreds digits takes place before the transmission of the tens and units digit impulses from the calling subscribers line. The dialing of tens and units digits controls, as in similar step-by-step systems, the vertical and rotary operations of the connector switch.

The control circuit of the group selector is immediately dissociated from the group selector after the thousands and hundreds digit record is transmitted to the control circuit of the connector while the latter control circuit is dissociated from the connector when the called subscriber removes the receiver from the hook to answer the call.

A clearer conception of the scope and purpose of this invention will be obtained from a consideration of the following description, taken in connection with the attached drawings in which:

Fig. 1 shows schematically a calling line, line switch and the circuit elements of a group selector of the Strowger type equipped with four wiper sets.

Fig. 2 shows schematically the circuit elements of a connector of the Strowger type equipped with four sets of wipers.

Fig. 3 shows a control circuit common to a plurality of group selectors with any one of which it may be operatively associated over the common leads extending from the lower margin of the drawing shown in Fig. l by the operation of relays X and K in the group selector circuit shown in Fig. 1.

Fig. 4 shows a control circuit common to a plurality of connectors with any one of i which it may be operatively associated over the common leads extending from the top margin of the drawing into the connector shown in Fig. 2.

Fig. 5 is a diagram showing howvthe several figures should be arranged to illustrate the complete circuits of the invention.

Each of the wiper sets of the group selector of Fig. 1 is wired to be connected to the calling line by the operation of one or more of relays A, B and C in combination with those which have not been operated, according to the wiper set to be utilized in establishing the connection. Thus, the uppermost set shown in the drawings and composed of wipers LJ, +LJ and TLJ is associated with the relay A operated; the second set composed of wipers Ll, +L1 and TLl with the relay C operated and relays B and A unoperated; the third set composed of wipers L2-, +1.2 and TL2 with the relay B operated and relays C and A unoperated and the fourth set -L3, +L3 and TL3 with the relays B and C operated and relay A unoperated. The test wipers TLJ, TLl, TL2 and TL3 are also wired to contacts of relay X for connections with other parts of the circuit, as described hereinafter, for the purpose of imposing the proper testing condition on the test wiper of the selected wiper set. The wiper set LJ, +LF and TLJ gives access to trunks leading to interconnecting oiiices whilst the three other wiper sets have access to local trunks extending to 400 point connectors.

Each of the wiper sets of the connector of Fig. 2 is wired to be connected to the talking circuit by the operation of one or more of relays 2W 2X and 2Y. Thus, the upper most set on the drawing 1, +1 and T1 is associated with relay 23V operated; the second set 2, +2 and T2 with relay 2X operated; the third set 3, +3 and T3 with relay 2Y operated and the fourth set 4, +4 and T4 with both relays 2X and 2Y operated. The test wipers T1, T2, T3 and T4 are wired through contacts of these relays for the purpose of association and selection with other parts of the circuit for imposing the proper test condition on the test wiper of the selected wiper set.

Referring now to the drawings, placed in the relative positions indicated by Fig. 5, the removal of the subscribers receiver causes a preselecting switch of any known type to connect with an idle group selector switch. At this time, it is assumed that the common control circuit associated with this group of selectors is idle. As already indicated, the preselecting switch is associated with a group selector only when such a selector can be operatively connected to the idle control circuit. During the time, therefore, that the control circuit is busy with any group selector, all other group selectors common to the busy control circuit will be made busy. Returning now to the originating call, the seizure of the group selector causes the operation of relays K and E in series from a ground in the presclecting switch, over the test terminal '1,

back contacts of the No. 1 contact set of relay A, back contacts of the No. 1 contact set of relay B, back contacts of the No. 2 contact set of relay C, normal contacts of the off-normal springs N1 of the group selector switch, both windings in parallel of relay K and both windings in parallel of relay E to battery. The quantity of current flowing through both of these relays during the operating time is greater than what it will be after they are fully operated since the lefthand winding of relay K is removed from the circuit I when the back contact of its'No. 2 contact set is broken and the righthand winding of relay E is removed when its No. 1 back contacts are broken. Once the relays are operated the above mentioned parallel windings are removed and both relays hold in series over one of their windings to ground on the test terminal, until a. locking ground is supplied to both relays from relay 3G as explained hereinafter.

Relay K operates relay X by ground on its No. 1 front contacts while relay E performs no useful function at this time. Relay X, on operating, closes through the four test wipers of the group selector to the control circuit and also closes through the connecting leads which operatively associate the selector with the control circuit. The pulsing relay D is now connected over the subscribers loop preparatory to pulsing in a circuit which may be traced as follows Battery through the lefthand winding of relay D, back contacts of the No. 2 contact set of relay 3R, front contacts of the No. 5 contact set of relay K, back contacts of the No. 3 contact set of relay B, back contacts of the No. 5 contact set of relay G, back contacts of the No. 3 contact set of relay A, the negative bank terminal and wiper of the preselecting switch, over. the subscribers loop, the positive wiper and bank terminal of the switch, back contacts of the No. 4 contact set of relay A, back contacts of the No. 4 contact set of relay B, back contacts of the No. 4: contact set of relay C, front cone tacts of the No. 6 contact set of relay K, back contacts of the No. 3 contact set of relay 3R, right hand winding of relay D, normally made contacts of the No. 5 contact set of relay F to ground on the normally made contacts of relay 3C. The operation of relay D operates slow-releasing relay G from ground on the front contacts of its No.2 contact set. Relay G is made slow releasing so that it will not follow the pulsing operations of relay D. Relay G supplies locking ground to relay K from its No. 3 front contacts through the No. 1 back contacts of relay R, normally made contacts of the No. 4 contact set of relay 3A to the right hand winding of relay-K, over the frontcontacts of its No. 2 contact set. Since relays K and E are connected in series this ground serves to hold both relays in an operated position. Relay G also extends ground to the test terminal T through its No. 1 front contacts and No. 1 front contacts of relay X. This ground, it will be noted, also extends back by way of the original path to the right hand winding of relay K, but it is only temporary as the operations described below will open the off-normal contacts N1 and remove it, thereby making relay K entirelydependent upon the locking ground furnished from relay Gr.

Belay D now responds to the impulses of the first digit dialed and on its first release closes a ground over the back contacts of its No. 2 contact set and the No. 5 front contacts of relay G to operate slow-release relay F. Relay F is made slow releasing so that itwill remain operated during the succession of pulses, but releases during the longer interval between digits. The ground for operating relay F is extended in parallel through the No. 7 back contacts of relay H and the No. 8 front contacts of relay to operate vertical magnet V. The magnet V, therefore, follows the pulses of the first digit and raises the switch shaft carryingthe four sets of wipers to a level corresponding to the digit dialed.

In order to provide proper operation of the pulsing circuit under conditions of dis torted pulses, the operation of relay F opens the circuit of relay D at the normally made contacts of the No. 5 contact set of relay F and an auxiliary circuit is substituted for it from the operated contacts of the vertical interrupter contacts VINT of the magnet V and the No. 1 contacts of relay D. This circuit extends through the No. 7 front contacts of relay K and the operated contacts of the No. 5 contact set of relay F. The function of this circuit is to insure that the vertical magnet always takes a complete step once relay D has released during the open period of the pulse. Should the open period be too short as a result of distortion or other line conditions, then the corresponding earlier closure of the subscribers loop will not cause an immediate reoperation of relay D since the original operating groundat relay 3C has been removedby the operation of relay F and magnet V may not have operated sufficiently to close its interrupter contacts. Relay D, therefore, remains deenergized even though the dialing circuit has reclosed and, in its normal position, continues to sup ply ground on the back contacts of its No. 2 contact set for operating vertical magnet V. When the magnet V has operated and a step thereby insured it closes the vertical interrupter contacts VINT supplying ground to relay- D which can now operate over the subscribers loop. Once relay D operates it locks to its No. 1 front contacts, replacing the ground on the contacts VINT, since these contacts will open when the vertical magnet deenergizes, which occurs when relay D oper ates. In this manner the vertical magnet is insured against receiving less pulses than is required for the pulses of the digit, due to disturbing line conditions.

lVhen the selector moves off normal, the off-normal contacts N1 are closed and a circuit is closed for operating relay N through the No. 4 front contacts of relay K, the contacts N1, back contacts of the No. 2 contact set of relay C, back contacts of the No. 1 contact set of relay 13, back contacts of the No. 1 contact set of relay A to ground on the conductor connected to terminal T. Relay N re mains operated for purposes which will be made clear by the operations described below until a wiper switching relay or relays A, B or C or B and C are operated or until the selector is released.

Local calis In the embodiment of the invention disclosed, it has been assumed that a five digit numbering system is employed in which the first digit discriminates between a local and an interoilice call. It is also assumed, in the present embodiment of the invention that the first digit zero signifies a local call as contrasted with any other value of the first digit which, as described hereinafter, signifies an interoi'iice call. VJhen the vertical shaft has been stepped to the tenth level for a local call operation, the switch sha t contacts NPl are closed on the tenth level thereby operating relay 313 through the No. 8 front contacts of relay K and No. 3 back contacts of relay 3A. The operation of relay 3B closes a circuit for release magnet Z through the front contacts of the No. 3 contact set of relay X, No. 4 front contacts of relay 3B to ground on the No. 2 back contacts of relay F. The operation of magnet Z releases the switch shaft and upon its dropping to normal, 011' normal contacts N1 are opened, causing the release of relay N. A circuit is now closed for relay 23A from ground on the No. 1 hack contacts of relay F, No. 1 front contacts relay 33, back contacts of the No. 1 contact set of relay N to battery through the winding of relay SA. Relay 3A looks over its No. 2 contacts to ground on relay E. It will he noted that the circuit for relay 3B is opened at the No. 3 back contacts of relay 311 so that, when this latter relay operates, relay 3B releases. However, since the circuit for relay 3A is controlled through the No. 1 front contacts of relay 3B, relay 3B is made slightly slow in releasing, so as to insure the full operation and locking of relay 3A before relay 3B releases. The operation of relay 3B is opened at this time so as to prevent its reoperation should the succeeding digit be of the same value as the one used to discriminate between an interoifice and a local call.

As before, relay D is now connected across the subscribers loop for further pulsing. lVhen the second or thousands digit is received, relay D responds to the pulses and the vertical magnet V is stepped accordingly. \Vhen the loop is opened at the first impulse, relay F operates as before in parallel not only with the vertical magnet V, but also with relay 3P which energizes over its left hand winding by way of the back contacts of the No. 6 contact set of relay 3W, back contacts of the No. 5 contact set of relay 38, back contacts of the No. 4 contact set of relay 3P, No. 6 front contacts of relay 3A, to ground at the back contacts of the No. 2 contact set of relay D. Relay 8P looks with both windings in series to ground on the No. 6 front contacts of relay G by way of its No. 9 front contacts and the No. 6 back contacts of relay 3S. Relay H also partially operates at this time by way of the back contacts of its No. 2 contact set and the No. 3 front contacts of relay F to ground on the No. 1 front contacts of relay 3A. The No. 1 light front contacts of relay H only are closed by the partial operation of relay H and short circuit the left hand winding to ground on relay G thus keeping relay H for the time being in this partially operated condition. lVhen relay D releases on the next or second impulse, relay 3S is partially operated through a path closed over the front contacts of the No. 4 contact set of relay 3P, the No. 6 front contacts of relay 3A to ground at the back contacts of the No. 2 contact set of relay D. The No. 3 light front contacts close and, when relay D reoperates, relay 3S will operate fully with both windings in series to ground on relay G by way of the back contacts of the No. 3 contact set of relay H and the No. 5 front contacts of relay 3P. The operation of relay 3S unlocks relay 3P at the No. 6 back contacts of relay 3S and closes a circuit to energize relay 8W over both windings via the No. 4 front contacts of relay 3H, and the No. 4 back contacts of relay H to ground on relay G. Relay 3V7 locks to ground on relay G by way of the normally made contacts of the No. 5 contact set of relay H and No. 6 back contacts of relay 8P. The release of relay 3P releases relay 33 at the No. 5 front contacts of relay 3P. Thus it is seen that the first impulse operates relay 31 while the second impulse operates relay 3lV and releases relay 31?. At the next or third impulse relay 31? is again partially operated by way of the back contacts of the No. 6 contact set of relay H, front contacts of the No. 6 contact set of relay 31V, back contacts of the No. 5 contact set of relay 33, back contacts of the No. 4 contact set of relay 3P, No. 6 front contacts of relay 3A to ground on relay D. When relay D reoperates at the termination of the third impulse, relay 3P operates fully to ground on relay G via its own N0. 9 light contacts and the No. 6 back contacts of relay 3S. This reoperation of relay 3P releases relay PTVV at the No. 6 back contacts of relay 31?. The fourth impulse operates relay 3S and relay 3V] and releases relay 3.]? as before; the cycle of operation repeating itself, relays 3P and 3W operating alternately so that if the digit is odd relay 3P remains energized and if even, relay 31V remains operated.

At the end of the digit relay F releases and removes at its No. ,3 front contacts the short circuit from the left hand winding of relay H causing this relay to operate fully over both windings in series and lock to ground on relay G. The operation of relay H opens at its No. 7 back contacts the circuit of the vertical magnet V so that this magnet is not affected by the third digit which is next received. Wit-h the closure of the No. 7 back contacts of relay F a circuit is closed for either relay L or relay M depending upon whether the digit just dialed was odd or even; that is, whether relay 3P or 3V7 was last energized. The circuit path extends from ground at the No. 7 back contacts of relay F through the No.9 front contacts ofrelay 3A,No. 3back contacts of relay M, No. 3 back contacts of relay L and either No. 8 front contactsof relay 3P or No. 7 fronticontacts of relay to battery through the winding of relay L or relay M. Relay L or relay M locks to ground on relay G.

We will assume that the second digit, by way ofillustration, was odd and that, inconsequence thereof, relays 3P and L were energized at the termination of that digit. The first impulse of the third or hundreds digit operates relay F and, in parallel with it, opcrates .relay 3S over the circuit path previously described. With relays F and H operated a circuit is closed for relay I through the No. 2 back contacts of relay 1, front contacts on the No. 2 contact set of relay H, No. 3 front contacts of relay F to ground on the No. 1 front contacts of relay 3A. Relay I partially operates at this time and remains in this condition until the end of the digit; the closure of its No. 1 light contacts short circuiting its right hand winding with ground from the contacts of relay Gr until the release of relay F as explained hereinafter. When relay F energizes, a circuit is also closed for relay 3X over the No. 2 back contacts of relay 3X, the No. 4 front contacts of relay F and the No. 1 front contacts of relay L to ground on the No. 1 front contacts of relay 3?. Relay partially operates at this time, closing its No. 1 light front contacts and short circuiting its right hand winding over the No. 5 back contacts of relay 3Y to ground on the No. 6 contacts of relay G. The operation of relay 3S unlocks relay 3P, thereby rem ving :theshc t circuit from the right hand winding of relay 3X, causing this relay to fully operate and lock with both windings in series to ground on relay Gr by way of the No. 5 back contacts of relay 3Y. The next or second impulse causes the operation of relay 81V from ground on the back contacts of the No. 2 contact set of relay D, the No. 5 contacts of relay G, No. t front contacts of relay 3A, back contacts of the No. 4 contact set of relay 3P, front contacts of the No. 5 contact set of relay 3S through the right hand winding of relay 3W to battery. Relay- 31V locksover both windings in series and its No. 5 front contacts via the front contacts of the N o. 5 contact set of relay H, the No. 3 back contacts of relay 3J, toground on relay G. The operation of relay 3W opens the circuit of relay 3S at its No. 3 back contacts, causing the latter relay to release. The next or third impulse operates relay SJ through the front contacts of the No. 6 contact set of relay H, front contacts of the No. 6 contact set of relay 3W, back contacts of the No. 5 contact set of relay 3S, back contacts of the No. 4 contact set of relay 3P, the No. 6 front contacts of relay 3A, the No. 5 contacts of relay G to ground on relay D. Relay 3J locks to ground o-nrelayGviaits No. 4 front contacts and the No. 7 back contacts of relay 3P. The operation of relay 3d opens the locking circuit of relay 3W at the No. 3 back contacts causing this relay to release. The fourth impulse now causes the operation of relay 3P over the path previously described and unlocks relay 3J at the No. 7 back contactsof relay 3P. Relay 3Y is also partially operated at this time through the No. 2 contacts, the front contacts of the No. 2 contact set of relay 3X, the No. 4 front contacts of relay F, No. 1 front contacts of relay L, to ground on the No. 1 front contacts of relay 31?. The closure of the No. 1 light contacts of relay 3Y servesto keep the left hand Winding short circuited to ground on relay G and thereby maintain the relay in a partially operated condition. The fifth impulse operates relay 3S and releases relay 3P. WVith the release of-relay 3P, the short circuit around the left hand winding of relay 3Y is removed atthe No. 1 front contacts of relay 3P causing relay BY to energize fully and look over the back contact of the #1 contact set of relay 3Z to ground on relay G with both windings in series while at its No. 5 back contacts it opens the lockingcircuit of relay 3X which releases at this time. Relay SY partially prepares a circuit for relay 3Z at its No. 6 front contacts and relay 3W energizes again on the sixth impulse releasing relay 38. On the seventh impulse relay 3J again operates releasing relay 3W. On the eighth impulse relay 3P energizes again releasing relay 3J and completing at the No. 1 front contacts of relay 3P the circuit of relay 3Z which partially operates and, on the ninth impulse when relay 3S operates and releases, relay 3P operates fully and locks to ground on relay G. On the tenth impulse relay 3W again operates releasing relay 3S. The operation of relays 3S, 3lV, 3J and SP takes place in the manner already described. The operation of relay 3Z also releases relay 31 at the back contacts of the No. 1 contact set ef relay 3Z. It will be seen, however, that if relay SP is energized by the last impulse of the digit and causes the half step operation of relay 3X, SY or 32, the relay whose half step operation last took place will operate fully when the No. 4: front contacts of relay F are opened by the release of this relay at the end of the digit.

If the second digit is even, relays 3W and M are energized at the end of the digit and relay 3X is partially operated over the No. 2 front contacts of relay 3W No. 1 front contacts of relay M, No. 4 front contacts of re lay F and back contacts of the No. 2 contact set of relay 3X. lVhen the third pulse is dialed, relay 3J is operated on the first impulse, relay 3P on the second, relay 38 on the third and so on, the relays 3X, 3Y and 3Z being energized in succession when relay 31V is operated and released in each cycle. The above cycle of operations may be tabulated as follows:

Table 2nd digit X Y Z 3rd d1 1t g Odd Even group (P-L) (WM) 1 S .T X 2 W P X 3 .T S X 4 P W X 5 S J Y 6 W P Y 7 J S Y 8 P W Z 9 S J Z 0 W P Z by both the second and third digits.

At the end of the third digit the release F removes at the No. 3 front contacts the short circuit from the right hand winding of relay I, causing this relay to operate fully at this time and lock with both windings in series to ground on relay G. The circuit of rotary magnet R is now closed over the rotary interrupter contacts RINT, the No. 9 front contacts of relay K, the No. 4 front contacts of relay I to ground on the No. 6

back contacts of relay F by way of front contacts of the No. 8 contact set of relay 3A and the back contacts of the No. 6 contact set of relay 3R. Relay I also connects test relay 3R to the test wipers TLl, TL2 or TL3 depending upon whether relays 3X, 3Y or 3Z is energized over the front contacts of the No. 7 contact set of relay 3A, the No. 3 front contacts of relay I, the No. 4 contacts of either relays 3X, 3Y or 3Z, the No.11 or No. 10 or No. 9 front contacts, respectively, of rclayXto the selected test wiper. When an idle connector is engaged, relay 3R operates, looks over its left hand winding to ground on relay G, opens the operating circuit of the rotary magnet R and closes a circuit from ground on the No. 4 front contacts of relay 3R. front contacts of No. 5 contact set of relay 3A. No. 3 front contacts of relay 3X or 3Y or 3Z and the No. 7 or No. 5 or No. 6 front contacts respectively of relay X for operating switching relay C or B or both relays C and B. The switching relay or relays lock to the test wiper and connect up the appropriate wiper set.

If all trunks in the wanted group are found busy by the group selector, the switch shaft will rotate to the 11th terminal where the contacts S1 are closed and relay 3C is energized. Busy tone is transmitted to the calling line through the right hand winding of relay D. When the calling subscriber restores his receiver, relays D, G, E, 3A and all other operated relays in the control circuit are released. Relays K, X and the wiper selecting relays A, B and C- are also released and a circuit is closed from battery through the winding of release magnet Z, the back contacts of the No. 3 contact set of relay X, No. 3 back contacts of relay C, No. 2 back contacts of relay B, No. 2 back contacts of relay A and off-normal ground contacts N2 are closed for the operation of release magnet Z which, on operating, restores the switch shaft to normal.

If an idle trunk is found however. relay 2K in 2 and relay BE in Fig. 4 are operated in a circuit from ground on the test wire over a previously traced path, the test wire. ha ck contacts of the No. 2 contact set of relay 2B, off-normal contacts N1. both windings in parallel of relay 2K and both windin gs in parallel of relay EE to battery. These relays, when operated, disconnect their right hand windings and hold to ground on the test conductor with their respective loft windings in series. Relay 2K associates the connector with the control circuit. The positi ye wire of the selected trunk is now extended over the back contacts of the No. 4 contact set of relay 2B, the No. 8 front contacts of relay 2K, the back contacts of the No. 2 contact set of relay 4E. No. 4 frontcontacts of relay EE, normally closed contacts of the No. 2 contact set of relay 4C and similar contacts of relay 4D to one terminal of the windings of relays 4C and 4D. The negative wire is extended over the back contacts of the No. 3 contact set of relay 213, No. 5 front contacts of relay 2K, back contacts of the No. 1 contact set of relay 4E, No. 2 front contacts of relay EE, normally made contacts of the No. 2 contact set of relay l-A and similar contacts of relay 413, to one terminal of the windings of relays 4A and LB. The other terminal of the windings of relays 4B and 4-D are connected to battery whilst the other terminals of the windings of relays 4A and 4C are con nected to ground on the No. 3 front contacts of relay EE.

Relay 3B, 3, disconnects the impulse relay D from the subscribers loop at the back contacts of its No. 2 and No. 3 contact sets, respectively and, by way of the front contacts of these contact sets connects the negative and positive wires of the selected outgoing trunk to one terminal of relays O and 3h, respectively. To the other terminal of these relays is connected battery and ground con ditions in accordance with the setup of relays 3S, 3W 3d and 3P. The circuits through these relay combinations are established to the negative and positive wires for effecting the registration in the connector control circuit for selecting the wiper set at the connector. If relay SP is operated both Wires are grounded at the No. 2 and No. 3 front contacts of relay 3P; if relay 38 is operated, battery is connected to both wires at the No. '1 and No. 2 front contacts of relay 35; if relay 3J is operated, battery is connected to the negative wire and ground to the positive wire by the No. 1 and No. Qfront contacts respectively of relay 3J if relay 3W is operated ground is connected to the negative wire and battery to the positive wire on the No. 1 and No. 4 front cont-acts, respectively of relay 3W.

In accordance with the condition set-up on the positive and negative conductors of the trunk, relays 413, 4D or 4A., 40 or 4B, 40 or LA, 4D, are operated and locked to ground on the No. 3 front contacts of relay E1 These relay combinations ground the leads to energize wiper switching relays 2V] or 2X or 21 or 2X and QY which connect up the appropriate Wiper set. Relays O and 3K, Fig. 3, also energize in series with the selected combination of relays and at their No. 1 back contacts open the holding circuits over which relay K, Fig. 1, and relay E, Fig. 8, are held energized. Relay'G will release a short interval after relayD has released and at its No. 3 front contacts opens another point in this holding circuit. The release of relay K switches through the subscribers loop to the connector, releases relay X and disconnects the group selector from the control circuit. In the control circuit all relays are restored to their normal condition by the release of relays G and E.

The operation of either relay 4A or 4B in combination with either relay 4C or 4D, closes a circuit for relay 4E and, when the subscribers loop is switched through, a circuit is closed for the impulse relay DD over the loop through the front contacts of the No. 1 and No. 2 contact sets of relay 4E to ground on the normally made contacts of the No. 2 contact set of relay FF and to battery on relay DD. Relay GG operates from the front contacts of theNo. 2 contact set of relay DD and front contacts of the No. 3 contact set of relay 4E. Relay GG supplies ground to the test wire and holding ground for relays 2K and EE. Relay FF, which also operates from the same front contacts of relay DD as did relay GG, closes a circuit from ground on the No. 3 back contacts of relay II through front contacts of the No. 3 contact set of relay FF to partially operate relay HH; this last relay on closing its No. 4 light contacts, keeps the right hand Winding short circuited to ground on the No. 5 contacts of relay EE. At the front contacts of the No. 2 contact set of relay FF an alternative ground is given to the left hand winding of relay DD from the VINT interrupter contacts of vertical magnet 2V When magnet 2V operates. This ground is supplied to the relay DD by Wayof the No. 7 front contacts of relay 2K, back contacts of the No. 2 contact set of relay HH, No. 2 front contacts of relay FF to the left winding of relay DD. This circuit arrangement is similar to the circuit arrangement previously described in connection with the impulse relay D in Fig. 3 in order to secure accurate operation of the pulsing' circuit under distorted line conditions. Relay GG is of the slow release type and is maintained operated during the impulse releases of relay DD.

The fourth or tens digit .is now dialed and causes the interruption of the circuit of relay DD. At the first impulse a circuit is closed for the vertical magnet 2V via the No. 6 front contacts of relay 2K, back contacts of the No. 1 contact set of relay HH, No. 1 front contacts of relay FF to ground at the back contacts of the No. 2 contact set of relay DD. At the first vertical step of the connector switch shaft a circuit from ground on the off-normal springs N2 and No. 4 front contacts of relay 2K operates relay 4N Which, at its front contacts, transfers the circuit of relay FF via No. 1 front contacts of relay FF to the back contacts of the No. 2 contact set of relay DD. Relay FF is of the slow release type and is maintained operated during dialing over this circuit but at the end of the fourth digit releases, and at the back contacts of the No. 3 contact set removes the short circuit from the right hand Winding of relay I-IH causing this relay to fully operate and look over both its windings in series to ground on theNo. 5 front contacts of relay EE. At

the front contacts of the No. 1 and No. 3 contact sets respectively of relay HH the impulsing circuit is transferred to the rotary magnet 23 which is now stepped by the fifth or units digit. During the receipt of the inipulses of this digit, relay FF is energized over the front contacts of the No. 3 contact set of relay HH and closes a circuit via the back contacts of the No. 3 contact set of relay II, front contacts of the No. 3 contact set of relay FF and front contacts of the No. 5 contact set of relay HH to operate slow release relay CC which, at its No. 1 front contacts, closes a circuit through right hand winding of relay II. This relay partially operates, closing only its No. 1 front light contacts at this time and short circuiting its left hand winding. After receiving the fifth digit impulses, relay FF releases, opening the circuit of relay CC which, however, does not release until after the expiration of a short interval during which the wanted line is tested over a circuit extending from the test wipers T1, T2, T3 or T4, through the appropriate contacts of relays 2W, 2X or 2Y depending on which set of wipers is selected, No. 13 front contacts of relay 2K, right hand winding of test relay RE, No. 2 front contacts of relay CC, back contacts of the No. 3 contact set of relay FF to ground on the No. 3 back contacts of relay II.

If the wanted line is busy, relay RR fails to operate and on the release of relay CO, relay II operates fully over both its winding in series to ground on the No. 5 front contacts of relay EE. This causes a busy tone to be transmitted to the calling line via the positive wire of the trunk by-pass condenser K and front contacts of the No. 2 contact set of relay II. When the calling party restores his receiver, relay DD deenergizes and opens the circuit of relay GG which, in turn, opens the holding circuit of relays 2K and EE. The release of relay EE opens the circuits of relays II and HH at its No. 5 front contacts causing these relays to release. The release of relay 2K disconnects the connector from the control circuit, causing the release of whatever switching relays 2W, 2X or 2Y, are operated, releases relay N and any of the operated relays 4A, 4B, 4C and 4D, and completes a circuit via the No. 15 back contacts of relay 2K, the No. 3 back contacts of relay 2D to ground and No. 7 back contacts of relay 2B for the release magnet 2Z. The removal of ground from the test conductor T causes the release of wiper switching relays A, B or C, Fig. 1, of the group selector and the previously described circuit is closed for the release magnet Z thereat.

If, however, the wanted line is idle, relay BB is operated before relay CC releases, locks up over its No. 3 front contacts to ground on the No. 5 front contacts of relay EE and closes a locking circuit over its No. 5

contacts for relay CC. Ringing current is new transmitted over the called line through ti o following circuit: ringing source, No. l front contacts of relay RR, No. 3 back contacts of relay 4F, right hand winding of ringing cutoff relay 4F, No. 12 front contacts of relay 2K, back contacts of the No. 6 contact set of relay 2B, selected negative wiper through the contacts of the appropriate switching relays 2W, 2X or 2Y, to and over the called line, selected positive wiper, back contacts of the No. 5 contact set of relay 213, No. 11 front contacts of relay 2K, No. 2 front contacts of relay RR to battery. Tell tale ringing current is sent to the calling subscriber over the No. 1 front contacts of relay RR, back contacts of the No. 2 contact set of relay II, by-pass condenser K, front contacts of the No. 2 contact set of relay 4E, N0. 8 front contacts of relay 2K, back contacts of the No. 4 contact set of relay 2B to the positive wire of the trunk.

When the called subscriber answers, relay F operates and locks over its left hand winding to ground on relay EE disconnects ringing current at its No. 3 back contacts and, at its No. 1 front contacts, closes a circuit to operate relay 2B. Relay 2B grounds the test wire T at its No. 2 front contacts, closes a holding circuit for the switching relay or relays 2W, 2X or 2Y or 2X and 2Y at the front contacts of the No. 7 contact set, opens the holding circuit for relays 2K and EE, thereby freeing the control circuit, extends the calling line to the front bridge relay 2A and the called line to back bridge relay 2D. Relay 2A closes a locking circuit for relay 2B.

When the calling subscriber restores his receiver, relay 2A releases, unlocking relay 2B which removes ground from the test wire T and causes the release of the group selector in the manner already described. When the called subscriber restores his receiver, relay 2D releases and closes the circuit for the release magnet 2Z as already described. Relay 2D is wired so as to short circuit the front contacts of the No. 5 and No. 6 contact sets of relay 213 so that if the called subscriber fails to restore, relay 2D remains operated holding operated the wiper switching relay and grounds the test brush to busy the connector to other incoming calls.

lnterofiice calls If the first digit is other than Zero it signifies an interofiice call and on the release of relay F at the end of the digit the test relay 3R is connected to the test wiper TLJ through the No. 8 front contacts of relay X, No. 2 back contacts of relay 313, back contacts of the No. 7 contact set of relay 3A, right hand winding of relay 3R to ground on the No. 6 back contacts of relay F. At the same time a circuit is closed for the rotary magnet B through the No. 9 front contacts of relay V the distant group selector, looks over its left hand winding throuo'h its No. biront contacts to ground on relay and opens the rotary magnet circuit at the back contacts of its No. 6 contact set. The right hand winding is short circuited, the short circuiting ground being transmitted to the test wiper of the group selector by the path previously described in the description of a local call so that the seized trunk will test busy to other hunting group selectors- It all trunks are busy the rotary magnet continues to rotate the wiper shaft untilthe 11th terminal is reached, whereupon the selector restores'to normal and busy tone istransmitted to the calling subscriber in the manner already described.

It a trunk is seized, a circuit for relay A is now closed at the No. t front contacts 01": relay 3R through the back contacts of the No.

5 contact set of relay 3A and the No. 4- fron't contacts of relay X. Relay A locks to ground on the test wire T over the No; 5 front contacts, switches'thesubscribers loop and test wire to th'e first wiper set Lil, +LJ and TLJ at the front contacts of the Nos. 3, i and 1 contact sets respectively and, at the back contacts of these sets, opens the loop and testwire to the control circuit. Relay I) now releases and causes the release of other relays in the control circuit as previously de scribed. The call proceeds from this point with pulsing operations in the groupselector at the distant ollice, the circuit operations being identical with those described for a group selector and a connector in alocal connection.

Although the group selector switching stage is shown arranged for oper'ation'with a discriminating first digit, such an arrangement is purely optional. It will be understood that the tour wiper sets of the selector may be arranged to give access to local trunks exclusively. In this case fourfdigits will be dialed, the first dig-it not being absorbed, and the circuits can be modified in such a manner that, in accordance with the values of the first and second digits, a particular one of the four wiper sets of the'selector and of the connector can be selected.

It will be noted also that in interofiice connections the number of lines to'which connec tions can be made by the use of two switching stages is necessarily restricted to the number which can be reached bya group of ten trunk levels in the upper bank of the group selector switching stage and ten connectors at the terminating ol'fice each of WlllCl'l will have accessib-il ity to 400 subscribers. Should it be desirable to expand the number of subscribers to be reached, itwill be necessary to introduce another group switching stage at-the terminating oflice. In case a two switching sta e interollice-call is to be made, the operations will take place as described above under a local call connection while, if a three switching stage, interoiiice call is to be made, the descriptionis covered above under interoilice calls.

What is claimed is: p

I. In an automatic telephone system, a first switch having a plurality of wiper sets, a second switch having a plurality of Wiper sets a register in said first switch for registering two digit series dialed therein to, means for directively setting said first switch in ac cordance with the first of these digit series and for selecting wiper set thereof in accordance with the setting of said registeran'd means controlled by said register for selecting a wiper set of sai-d second switch;

2. In an automatic-telephone system, a first switch having a plurality of wiper sets, a second-switch having a plurality of wiper sets, a first control circuit associated with said first switch, a second" control circuit associated with said second switch, means for registering in said first control circuit two digit series dialed thereinto-, means for selooting a wiper set in said first switch in accordance with the registration'of the second digit of said two digit series, a trunk line connecting said first switch with said second switch over said selected wiper set, means in said first control circuit for transmitting special signals over said trunk in accordance with the registration of said two digits, means in said second control circuit for registering said special signals and means in said second control circuit for selecting a wiper set in said second switch in accordance with the registration of said signals.

3. In an automatic telephone system, a first switch having a pl'ur-ality of wiper sets, a second switch having a plurality of-wiper sets, a first register circuit associated with said first switch, a second registercircuit as sociated with said second switch, means in said first register circuit for selecting a particular wiper set in the associated first switch, means including said first switch and said second switch for transmitting wiper selecting signals from said first register circuitto said second register circuit and means in said second register circuit for causing the selection of a particular wiper set in said second switch in accordance with said signals.

l. In an automatic telephone system, a first switch having a switch shaft carrying a plurality 'oaf wiper sets, a control circuit assoe ciated with said first switch, means in said control circuit for registeringimpulses of the second and third digit series dialed. therein to, means in said switch for vertically dis placing said shaft by impulses of the first digit series dialed, means for selecting awiper set in accordance with the number of the impulses of said first digit series, means for restoring said shaft to normal when said first series contains a predetermined number of impulses and means in said switch and said control circuit for further controlling the s lection of a wiper set and the vertical displacement of said switch shaft in accordance with impulses of said two succeeding digits registered in said control circuit when the number of impulses of said first digit contains said predetermined number of impulses.

5. In an automatic telephone system, a first switch having a plurality of wiper sets, a second switch having a plurality of wiper sets, a first control circuit associated with said first switch, a group of relays in said control circuit for registering two digit series dialed thereinto, and means for controlling wiper selecting operations in said first and second switches in accordance with the registration set up on said group of relays.

6. In an automatic telephone system, a switch having a plurality of wiper sets, a control circuit associated with said switch, means in said control circuit for registering two series of impulses comprising two digits of a wanted number and means in said control circuit for controlling the selection of a particular wiper set in said switch in accordance with the number of impulses in the second digit of said two digits.

7 In an automatic telephone system, a switch equipped with a switch shaft having a plurality of wiper sets, means in said switch for vertically stepping said switch shaft, a control circuit associated with said switch, means for registering in said control circuit two digit series dialed thereinto and means in said control circuit for vertically stepping said wiper shaft as many steps as there are impulses in said first digit.

8. In an automatic telephone system, a switch having a plurality of wiper sets, a control circuit associated with said switch, means in said control circuit for responding to dialed impulses, means in said control circuit for recording two series of said impulses and means in said control circuit for controlling the selection of a particular wiper set in said switch in accordance with said second series of said impulses.

9. In an automatic telephone system, a first switch having a plurality of wiper sets, a second switch having a plurality of wiper sets, a first control circuit associated with said first switch, a second control circuit associated with said second switch, means in said first control circuit for registering therein two digits of a wanted number, means for selecting a wiper set in said first switch in accordance with said registration, a trunk line connecting said first switch with said second switch over said selected wiper set, means for connecting said selected wiper set with said trunk line, means in said first control circuit for transmitting special signals to said second control circuit, and means in said second control circuit for recording said special si nals for controlling wiper selection in said second switch during the interval between the seizure of said trunk line and the commencement of the transmission of impulses for setting the selected wiper set of said second switch.

10. In an automatic telephone system, a first switch having a plurality of wiper sets, a second switch having a plurality of wiper sets, a first control circuit associated with said first switch, a second control circuit associated with said second switch, a group of relays in said first control circuit for registering impulses of two digits dialed thereinto, a group of relays in said second control circuit controlled by said group of relays in said first control circuit, means for selecting a wiper set in said first switch in accordance with the setting of said group of relays of said first control circuit, a trunk line connecting said first switch with said second switch, 1

means for connecting said first switch with said second switch over said selected wiper set and said trunk line, means controlled by the said group of relays in said first control circuit for selectively connecting electric potentials over said trunk line for setting said group of relays in said second control circuit, and means controlled by the group of relays in said second control circuit for select ing a wiper set in said second switch.

11. In an automatic telephone system, a switch having a plurality of wiper sets, a control circuit associated with said switch, a relay register in said control circuit comprising a first and second group of relays, and means for operating said first group of relays successively and cyclically by two series of impulses.

12. In an automatic telephone system, a switch having a plurality of wiper sets, a control circuit associated with said switch, a relay register in said control circuit comprising a first and second group of relays, means for operating said first group of relays successively and cyclically by two series of impulses, means for controlling the operation of said second group of relays by said first group of relays and means for selecting a particular wiper set in said switch by the setting of said second group of relays.

13. In an automatic telephone system, a first switch having a plurality of wiper sets, a second switch having a plurality of wiper sets, a control circuit associated with said first switch, a relay register in said con trol circuit comprising a first and second group of relays, means for operating said first group of relays successively and cyclically by two series of impulses, means for locking one of said relays in said first group at the termination of the second of said two series of impulses, and means for selecting a wiper set of said second switch in accordance with operated relays in said first group of relays.

14:. In an automatic telephone system, a group of first switches each having a plurality of wiper sets, a group of second switches each having a. plurality of wiper sets, a first control circuit common to said group of first switches, a second control circuit common to said group of second switches, means in each of said first switches for associating said first control circuit with any one of said first switches, means in each of said second switches for associating said second control circuit with any one of said second switches, means for registering in said first control circuit two digit series dialed thereinto, means for selecting a wiper set in said first switch in accordance with the registration of the second digit of said two digit series, a trunk line connecting said first switch with said second switch over said selected wiper set, means in said first control circuit for transmitting special signals over said trunk in accordance with the registration of said two digits, means in said second control circuit for registering said special signals, and means in said second control circuit for selecting a wiper set in said second switch in accordance with registration of said signals.

15. In an automatic telephone system, a group of first switches each having a plurality of wiper sets, a group of second switches each having a plurality of wiper sets, a first control circuit common to said group of first switches, a second control circuit common to said group of second switches, means in each of said first switches for associating said first control circuit with any one of said first switches, means in each of said second switches for associating said second control circuit with any one of said second switches. and means in said first control circuit for selecting a particular wiper set in the associated first switch and a particular wipe-r set in said second switch of said group of second switches associated with said second control circuit.

16. In an automatic telephone system, a group of switches each having a switch shaft carrying a plurality of wiper sets, a control circuit common to said group of switches, means in each of said switches for associating said control circuit with any one of said switches, means in said control circuit for registering impulses of the second and third digit series dialed thereinto, means in said switch for vertically displacing said shaft by r impulses of the first digit series dialed, means for selecting a wiper set in accordance with the number of impulses of said first digit series, means for restoring said shaft to normal when said first digit contains a predetermined number of impulses, and means in said switch and said control circuit for further controlling the selection of a. wiper set and 7 vertical displacement of said switch in accordance with impulses of said two succeeding digits registered in said control circuit when the number of impulses of said first digit contains said predetermined number of impulses. 17'. In an automatic telephone system, a group of first switches each having a plural ity of wipersets, a group of second switches each having a plurality of wiper sets, a. first for setting up a connection.

18. In an automatictelephone systenna 7 group of switches each having a plurality of wiper sets, a control circuit common to said group of switches, means in each of said switches for associating said control circuit with any one of said switches, means for registering in said control circuit two: series of impulses comprising two digits of a wanted number, and means in said control circuit tor controlling the selection of a particular wiper set in said switch in accordance with the number of impulses in the second digit of said two digits.

19. In an automatic'telephone system, a group of switches each equipped with a switch shaft having a plurality of wiper sets, means in each of said switches for vertically s'teppingsaid shaft, a control circuit common to said-group of switches, means in each of said switches for associating said control circuit with any one of said switches, means for registering in said control circuit two digit series dialed thereinto, and means in said control circuit for vertically stepping said wiper shaft as many steps as there are impulses in said first digit.

20. In an automatic telephone sysiem, a group of switches each equipped with a plurality of wiper sets, a control circuit common to said group of switches, means in each of said switches for associating said control circuit with any one of said switches, means in said control circuit for responding to dial impulses, means in said control circuit for recording two series of said impulses, and means in said control circuit for controlling the selection of a particular wiper set in said switch in accordance with said second series of said impulses.

21. In an automatic telephone system, a group of switches each having a plurality of wiper sets, a control circuit common tosaid switches, means in each of said switches for associating said control circuit with any one of said switches, a relay register in said control circuit comprising a first and second group of relays and means for operating said first group of relays successively and cyclically by two series of impulses.

22. In an automatic telephone system, a group of switches each having a plurality of wiper sets, a control circuit common to said group of switches, means in each of said switches for associating said control circuit with any one of said switches, a relay register in said control circuit comprising a first and second group of relays, means for operating said first group of relays successively and cyclically by two series of impulses, means for controlling the operation of said second group of relays by said first group of relays, and means for selecting aparticular wiper set in said switch by the setting of said second group of relays.

23. In an automatic telephone system, a group of first switches each having a plum rality of wiper sets, a group of second switches each having a plurality of wiper sets, a control circuit common to said first switches, means in each of said first switches for associating said control circuit with any one of said first switches, a relay register in said control circuit comprising a first and second group of relays, means for operating said first group of relays successively and cyclically by two series of impulses, means for locking one of said relays in said first group at the termination of second of said two series of impulses, and means for selecting a wiper set of said second switch in accordance with operated relays of said first group of relays.

24. In an automatic telephone system, a switch having a plurality of wiper sets, means in said switch for stepping said shaft vertically, a control circuit common to a plurality of said switches, means in said control circuit for responding to impulses transmitted thereinto, means in said control circuit for stepping said shaft by said impulses, and means in said control circuit to insure '55 one step to said shaft for each impulse of said impulses.

In witness whereof, I hereunto subscribe my name this 29th day of January, 1930.

JOHN HENRY ELVIDGE BAKER. 

